The process of pipe bursting to replace buried frangible pipes has been in commercial existence since the late 1980's. While originally developed with the intent of replacing cast iron natural gas pipelines in Europe, it is of great promise within the continental U.S. to remedy problems with sewer systems.
Our sanitary sewer systems are constantly a source of contamination for freshwater ecosystems. Ground water, present in great abundance after rainfall around sewer pipes actually enters the sewer system. It will enter the system as it has ingress through gaps, fractures and other leaks in the old and deteriorated pipes present in all older systems. By entering the sanitary system, the groundwater must be treated as sanitary waste.
Unfortunately, the rate of inflow of groundwater after a rainfall is often 2 to 4 times the systems normal flow rate. When this happens, the processing rate can't keep up with the inflow rate, the untreated sewage must be discharged back into the ecosystem, normally finding it's way to a freshwater lake or stream. It is after this type of event that ‘No Swimming’ signs are posted at beaches and other warnings are made by news media about raw sewage flowing into water ways.
There are four remedies for this problem. The first is traditional open cutting, digging of open trenches to replace the old leaking pipes. It has an excellent end product, however it involves massive disruption on the surface and is generally an unpopular solution. The second involves digging of ‘deep tunnels’, nothing more than storage caverns for excess flow that is intended to be treated at a later date. This works until rain storms occur back to back and the capacity is exceeded. In addition, the condition or leak rate of the sanitary system is always increasing as the pipes age.
The third and fourth methods are variations of each other. In lining, whether cured in place pipe (CIPP) or slip lining, the pipe is temporarily patched. It stops the leak for a period of years, but in general it is a ‘spot’ repair, or nothing more than a thin liner. It is inevitable that the process will have to be undertaken again when the next aging joint in the system begins to open and permit leakage.
The fourth method, the most permanent, most adaptable and unquestionably the overall preferred method, is pipe bursting and replacement of sanitary sewer systems. It produces a brand new pipe with superior life and sealing capability. It is a trenchless process much as CIPP or lining is, producing little surface disruption; however, it has suffered the drawback of involving more physical labor than lining.
The present invention provides a device that reduces the amount of physical labor required to perform pipe bursting of sanitary sewer systems. Such a process most typically uses a pneumatic impact device to hammer a mole through the existing pipe and expand the surrounding soil. This mole is commonly attached to the HDPE (high density polyethylene) product pipe that becomes the new, leak proof pipe system. The mole is pulled through the old pipeline by a winch mounted at the receiving end of the line, with or without use of an impactor in addition to the pulling force exerted by the winch.
In many processes, a pneumatic impact hammer is used as the mole. To maintain progress of a pneumatic hammer towing a string of plastic replacement pipe, the hammer is normally guided by a wire rope drawn by a constant tension winch. The winch is at ground level, with a mast that extends downward from the winch into either a small excavation, or more likely a sewer manhole. This mast is a hollow tube through which the wire rope passes to reach the subterranean level of the pipe. After changing direction 90 degrees around a sheave, the wire rope will enter the pipe and traverse the entire length of the pipe to be burst and replaced.
The constant tension winch has the formidable task of keeping suitable tension (in this case 24,000 lb) on the wire rope, and winding the wire rope for storage between jobs while functioning with the mast and sheave described earlier. In addition, the unit must be mobile. Upon completion of a section of pipe bursting (typically 500 feet), the winch must move rapidly to the next section. It is desirous, but has not been the case, that setup and teardown of the winch and mast should be rapid and with a minimum of effort. This invention addresses that aspect of the process, and in doing so, makes the process of pipe bursting more efficient, more cost effective and more likely to be chosen as a rehabilitation method over other methods described.
Previous designs involved the assembly of mast sections on the surface, then lowering the mast into position using a lifting device such as a small mobile crane. After the mast was in position in the manhole, the winch was brought into place and the mast attached to the winch. Upon completing this, the wire rope was threaded through the hollow sections to the sheave. At this point the unit would be considered ‘set up’. The process was performed in reverse to remove the winch upon completion of a pull.
Winches currently in use for underground pipe replacement generally include the Hydroguide series of winches sold by Vermeer. Handford U.S. Pat. No. 5,328,297 describes a pipe replacement system using a winch wherein the winch mast is deployed by lowering one of a pair of nested mast sections. This represents an advance over systems requiring complete manual assembly, but the job of deploying the mast and removing it when the job is completed is still a manual task.